well I know that when your busy with modeling you will find it easy to convert to subD and tweek a little there... from what I've heared...the smooth (not SubD) is better! but in that mode you'll not to be able to tweek or model further...

what I do when im modelling in polys...I just convert back and forth from poly to subd.... and sometimes when I want to see how it looks I just smooth it and go a couple of steps back to the polymode... You don't want to go to smooth and than delete the history!! but you'll need to verify this by a more advanced artist

well keep it going